Preparation of salts of 2-ketoaldonic acids



Patented June 11 1940 UNITED STATES J PATENT OFFICE F p 2,203,923; l 3 i PREPARATION OF SALTS F Z-KET'O- a ALDONICACIDS Richard Pasternack, Brooklyn, N. Y., and Peter P. Regna, North Bergen, N. J., assignors to e Charles Pfizer & Company, Brooklyn, N.Y., a.

j i i i corporation of New Jersey No Drawing. Application August-f5, 1939,

Serial No. 288.571

The object of this invention is the preparation of salts of 2-keto-aldonic acids by a simplified process giving improved yields. It is a continuation-impart of our copending application Serial No. 247,644, filedDecember 24, 1938 which has matured into Patent Number 2,188,777.

In said earlier application it is disclosed that aldonic acids and salts of aldonic acids may be oxidized by .chlorates the presence of vanadium catalysts in acidified aqueous media. We have now found that aconsiderable improvement in yield and a simpler recovery of the product is possible by the addition of a watermiscible organic solvent which is substantially inert to the oxidizing action of chlorates in the presence of vanadium catalysts. We prefer to use methyl alcohol in such quantity as to form an aqueous solution containing 50-70% by volume of the. methanol. From such a solution a substantial proportion of the dehydrogenated product is directly precipitatedduring, the reaction. The medium should beslightly acid; phosphoric acid or acetic acid are suitable acidifying agents. The vanadium catalyst may be added in solid form or may be previously dissolved in alkali or acid. Its'state of oxidation is of no importance, since in any case it is oxidized to the pentavalent state by the chlorate. Example 1.The dehydrogenation of sodium Z-idonate to sodium 2-keto-Z-idonate. To a solution of 21.8 g. of sodium Z-idonate in 45 ml. of water, 3.6 g. of sodium chlorate and 2 ml. 85% phosphoric acid were added. The mixed solution was slightly warmed and diluted with 120 ml. methyl alcohol. After the further addition of 2 g. of vanadium pentoxide, the cooled mixture was shaken for 3 to 4 days at room temperature.

As the oxidation proceeded, substantial 4o amounts of sodium Z-jketo-idonate crystallized out, since in aqueous alcoholthe sodium salt of the Z-keto-idonate is less soluble than sodium idonate. The end of the reaction is readily recognized by a color change of the solution from 45 yellow to green.

The vanadium catalyst was removed by' the following procedure: Sufficient water was added to. redissolve the precipitated sodium 2-ketoidonate and the mixture filtered to remove the 5 insoluble portion of the catalyst. The filtrate was then freed of alcohol by distillation under reduced pressure. The remaining aqueous solution was treated with sufiicient calcium ferrocyanide to precipitate the vanadyl ion and fil- 55 tered. The calcium remaining in solution was following. manner:

treated with the calculated amount of sulfuric 7 Claims. (01. eco -535) removed by treatment with oxalic acid and subsequent filtration. i l

To determine the amount of 2-ketoacid produced, an aliquot portion of the clear filtrate was analyzed by the usual Fehlings reduction meth- 0d. The indicated yield of z-keto-l-idonic acid was 85%. l

The main portion of the reaction mixture,

after concentration under diminished pressure which constants agree Well with the values given by Micheel, Kraft and Lohmann (Z. Physiol. Chem. 225: 13-27, 1934).

Ezcample 2.- -Preparation of the methyl ester of 2-keto-gluconic acid from ammonium gluconate. A solution containing 21.3 g. of ammonium d-gluconate in 100 ml. water wastreated with 3.6 g. of sodium chlorate, 2 ml. of 85% precipitate, consisting of 2-keto-gluconate and 3 catalyst, was filtered out and treated withwater.

. The insoluble catalyst was removed and the filtrate combined with the main solution.

This

soluble vanadyl ion was removed with calcium 1 ferrocyanide, and the calcium ion with oxalic acid. An analysis by Fehlings reduction on an aliquot portion showed a 72% yield calculated as ammonium 2-keto-gluconate.

This salt can be isolated by fractional crystallization or recovered as the methyl ester in the The reaction mixture is acid to combine with the ammonium salts to form ammonium sulfate. The solution is evaporated to dryness and the residue taken up with methyl alcohol.

ester crystallizes on standing. The melting point 1731'75 C. and rotation in water, at equilibrium (0, 2.8), agree with the values given by Ohle (Ber. 63: 849, 1930).

Our process is applicable to the aldonates in general, subject only to the limitation that the salt selected for dehydrogenation must be to some extent soluble in the particular concentration'of organic solvent present. Thus in the caseof the gluconates for example, it is preferable to use their alkali metal salts rather than their alkaline earth metal salts.

The invention claimed is:

1. Process which comprises treating a soluble aldonate with a member of the group consist- .ing of alkali metal and alkaline earth metal aldonate with sodium chlorate in the presence of a vanadium catalyst and in a mildly acid aqueous solution comprising essentially methyl alcohol.

4. Process for preparing 2-keto-a1donates which comprises reacting sodium chlorate upon a soluble aldonate in the presence of a vanadium catalyst and in a mildly acid aqueous solution comprising essentially methyl alcohol.

5. Process for preparing sodium 2-keto-Z- idonate which comprises reacting sodium chlorate upon sodium l-idonate in the presence of a vanadium catalyst and in a mildly acid aqueous solution comprising essentially methyl alcohol.

6. Process for preparing ammonium Z-ketogluconate which comprises reacting sodium chlorate upon ammonium gluconate in the presence of a vanadium catalyst and in a mildly acid aqueous solution comprising essentially methyl alcohol.

7. Process which comprises treating a soluble aldonate with sodium chlorate in the presence of a vanadium catalyst and in a mildly acid aqueous solution comprising essentially methyl alcohol from which a substantial proportion of the resulting 2-keto aldonate crystallizes during the reaction, and continuing until the solution changes in color from yellow to green.

RICHARD PASTERNACK. PETER P. REGNA. 

